The present invention relates to agricultural harvesters and, more particularly, to means for sensing the presence of grain in a crop flow at a particular location inside the harvester.
The operator of a harvesting machine such as a combine harvester is seeking a high harvester speed while keeping crop losses at a reasonable level. Therefore he needs information on the amount of grain which does not reach the grain tank and is deposited onto the field is behind the combine. To this end the combine is provided with sensors adjacent the components which carry the straw and chaff to the outlet of the machine. For instance sensors may be provided at the end of the upper sieve and at the end of the separation apparatus, e.g. straw walkers or a separation concave as shown in EP-A-0.117.587. The sensors commonly comprise a sensing plate and an associated impact detector as illustrated by EP-A-0.339.142.
Similar sensors may also be used for providing an indication of the crop flow rate at various locations of the combine as described in EP-A-0.631.906.
It has been experienced that the grain detection signal from an impact sensor next to a separation concave is easily jammed. A position close to the concave seriously hampers the crop flow, such that the area between the concave and the detection surface may get plugged by straw particles. Eventually the grain kernels no longer impact the plate and no useful signal is received. A more remote position of the impact plate reduces the plugging risks, but also reduce the number of kernels that reach the plate, thereby diminishing the quality of the sensor signal.
Accordingly,there is a need for a sensor apparatus which, provides a good indication of the grain losses and which is not prone to plugging.
According to the present invention there is provided a combine harvester comprising:
a main frame;
a threshing and separating arrangement mounted to said main frame and including, a threshing or separating rotor co-operating with a curved threshing or separating concave; and
a grain sensor having a grain detection surface, directed to a section of said concave to directly receive part of the crop flow from said concave and to provide a signal indicative of the quantity of grain kernels in said crop flow;
characterised in that said the plane of said detection surface and the plane tangent to said concave section intersect at an acute angle.
This arrangement provides for sideways deviation of the material flow from the concave such that it does not accumulate between the concave and the sensor surface. Any straw portions sticking through the concave mazes and held back by the sensor equally is forced sideways, thereby precluding false impact signals from the straw tips ticking again st the surface.
The intersecting angle may be substantially equal to 18xc2x0. The detection surface may also be inclined to both the horizontal and the vertical plane. Its central normal may extend through the axis of the rotor in order to receive an appropriate crop flow sample. The sensor may be disposed between the concave and an adjacent wall, where it is less subject to an air flow from the cleaning system. Preferably the sensor is attached to the frame or wall of the harvester by means of a support that has a minimal volume in order to prevent accumulation of stray material on the support. For instance the sensor may be mounted to a tubular support. The electrical conductors to the sensor may then be mounted inside the support, such that the crop material cannot hook behind.